Energy consumption worldwide is generally increasing, and conventional hydrocarbon resources are being consumed. In an attempt to meet demand, the exploitation of unconventional resources may be desired. For example, highly viscous hydrocarbon resources, such as heavy oils, may be trapped in sands where their viscous nature does not permit conventional oil well production. This category of hydrocarbon resource is generally referred to as oil sands or heavy oils. Estimates are that trillions of barrels of oil reserves may be found in such oil sand formations.
Recovery of highly viscous hydrocarbon resources may be enhanced by heating the oil in-situ to reduce its viscosity and assist in movement. One approach is known as Steam-Assisted Gravity Drainage (SAGD). The oil is immobile at reservoir temperatures, and therefore, is typically heated to reduce its viscosity. In SAGO, pairs of injector and producer wells are formed to be laterally extending in the ground. Each pair of injector/producer wells includes a lower producer well and an upper injector well. The injector/production wells are typically located in the payzone of the subterranean formation between an underburden layer and an overburden layer.
Another approach for heating the oil is based on the use of radio frequency (RF) energy. U.S. Pat. No. 7,441,597 to Kasevich discloses using an RF generator to apply RF energy to an RF antenna in a horizontal portion of an RF well positioned above a horizontal portion of an oil producing well. The viscosity of the oil is reduced as a result of the RF energy, which causes the oil to drain due to gravity. The oil is recovered through the oil/gas producing well.
Instead of having separate RF and oil/gas producing wells, U.S. Published Patent Application No. 2012/0090844 to Madison et al. discloses a method of producing upgraded hydrocarbons in-situ from a production well. The method begins by operating a subsurface recovery of hydrocarbons with a production well. An RF absorbent material is heated by at least one RF antenna adjacent the production well and used as a heated RF absorbent material, which in turn heats the hydrocarbons to be produced.
Another method for heating heavy oil directly inside a production well is disclosed in U.S. Published Patent Application No. 2012/0234536 to Wheeler et al. The method disclosed in Wheeler et al. raises the subsurface temperature of heavy oil by utilizing an activator that has been injected below the surface. The activator is then excited using at least one RF antenna adjacent the production well, wherein the excited activator then heats the heavy oil.
Instead of placing the RF antenna adjacent the production well, the RF antenna may be placed within the production well, as disclosing in U.S. Published Patent Application No. 2007/0137852 to Condsidine et al. In Condsidine et al., a combination of electrical energy and critical fluids with reactants are placed within a borehole to initiate a reaction of reactants in the critical fluids with kerogen in the oil shale thereby raising the temperatures to cause kerogen oil and gas products to be extracted as a vapor, liquid or dissolved in the critical fluids. The hydrocarbon fuel products of kerogen oil or shale oil and hydrocarbon gas are removed to the ground surface by a product return line. An RF generator provides RF energy to an RF antenna within the production well.
The use of RF energy to recover hydrocarbon resources increases the capital cost and operating cost for a hydrocarbon resource recovery apparatus. Consequently, there is a need to improve upon the use of applying RF energy to heat hydrocarbon resources within a subterranean formation.